Crop and soil factors of importance for the distribution of plant species on arable fields in Denmark

Analyses of spatial variation in multi-species weed communities together with environmental factors may be useful as a tool for developing sustainable long-term weed control and to better understand the ecology of weed species. We present an analysis of species recorded in 491 Danish fields surveyed in 2001-2004 distributed in 11 common agricultural crops. By using cluster analysis and canonical correspondence analysis (CCA) we identify crops that resemble each other with respect to their associated flora. By CCA, correlation and regression analyses we illustrate how the incidences of 40 common species relate to each other and can be related to important soil factors measured in the uppermost 20 cm. Clay content, pH, phosphorous, exchangeable potassium and magnesium, total nitrogen and carbon content in the soil were estimated. Based on weed frequency the cluster analysis separates the perennial crop (grass leys) from the annual crops (largest distance) and further, winter from summer annual crops. The cluster and correlation analyses reveal which plants usually occur together. The regression analyses showed that P and clay were the most important of the measured factors affecting the occurrence of the species and indicated the importance of the different soil factors for the occurrence of each of the 40 species. This study highlights how crop type and some important growing conditions affect the weed communities in Danish fields. Identification of key factors for the distribution of weed species may be used to improve weed control but may also be valuable for understanding weed communities and for creating a higher biodiversity in arable land. (C) 2009 Elsevier B.V. All rights reserved.